Many production processes involve the movement of partially processed subassemblies. It may be that while units have completed one step in a process, it is necessary to store them temporarily before they can be moved to the next step in the production process. Sometimes it is important that individual partially processed units not touch each other while in an intermediate state. It may also be that it may be desirable to be able to track and sort individual units, whether by particular properties, by age, by size, or other criteria. It may also be important to know and control the physical orientation of an object to facilitate a subsequent processing step.